1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and more particularly to an LCD device having red, green, blue and white sub-pixels arranged in a matrix pattern.
2. Discussion of the Related Art
As the society has entered in earnest upon an information age, flat panel display devices, which have excellent capabilities of a thin profile, light weight and low power consumption, and so on, are introduced. For example, the flat panel display devices include an LCD device, a plasma display panel (PDP) device, a vacuum fluorescent display (VFD) device and an electroluminescent display (ELD) device.
Among these devices, LCD devices are widely used for notebook computers, monitors, TV, and so on instead of a cathode ray tube (CRT), because of their high contrast ratio and characteristics adequate to display moving images.
The LCD device uses optical anisotropy and polarization properties of liquid crystal molecules. The liquid crystal molecules have a definite alignment direction as a result of their thin and long shapes. The LCD device includes a liquid crystal panel as an essential element. The liquid crystal panel includes a pair of substrates. On each of the substrates, first and second electrodes are formed to generate an electric field. The alignment direction of the liquid crystal molecules can be controlled by application of the electric field across the liquid crystal molecules. As the intensity or direction of the electric field is changed, the alignment of the liquid crystal molecules also changes. Since incident light is refracted based on the orientation of the liquid crystal molecules due to the optical anisotropy of the liquid crystal molecules, images can be displayed by controlling light transmissivity.
The liquid crystal panel includes first and second substrates and a liquid crystal layer interposed therebetween. An array element is formed on the first substrate. The first substrate may be called as an array substrate. Gate and data lines cross each other such that pixels arranged in a matrix shape are defined. A thin film transistor is formed at a crossing portion of the gate and data lines and is connected to a pixel electrode in the pixel region. In addition, a color filter element, for example, a color filter layer, a common electrode, and so on, is formed on the second substrate. The second substrate may be called as a color filter substrate.
FIGS. 1A and 1B are schematic plan views illustrating a pixel arrangement of the related art LCD device.
FIG. 1A shows a vertical stripe type pixel arrangement. In FIG. 1A, red (R), green (G) and blue (B) sub-pixels, which are defined by crossing gate and data lines, are alternately arranged along a horizontal line. The R, G and B sub-pixels constitute a pixel unit.
FIG. 1B shows a quad type pixel arrangement. In FIG. 1B, R, G, B and white (W) sub-pixels are arranged in a matrix pattern. The R, G, B and W sub-pixels constitute a pixel unit. The LCD device having the quad type pixel arrangement further includes the W sub-pixel. Accordingly, the LCD device having the quad type pixel arrangement has an improved white brightness. Each of the R, G, B and W sub-pixels has the same area as one another. Namely, an area of the W sub-pixels is 25% with respect to an entire area.
In the quad type pixel arrangement, the white brightness is improved. However, since an area of the R, G and B sub-pixels is reduced, brightness of pure color in R, G and B colors is decreased. Particularly, a visual sensitivity in a yellow color is distinguishably decreased. The yellow color is very sensitive such that an image quality is deteriorated because of decrease of the yellow color sense. In addition, a brightness difference between gray and white colors is increased due to increase of the white brightness, so that an image quality is further deteriorated.